Polymers adaptable for wire enamels

ABSTRACT

A polyester, a polyester/polyamide or a polyester/polyamide/polyimide polymers are prepared from (a) a diaryl terephthalate or diaryl isophthalate, and (b) an aromatic polyol or of (a) and a mixture of (b), and an aromatic diamine, or of (a), (b), (c), and (d) a triaryl mellitate, or a copolycarbonate of any of the foregoing including units derived from (e) a diaryl carbonate. The resulting polyester, polyamide, polyester/polyamide or polyester/polyamide/polyimide polymers are adapted for use an an insulating coating on an electrical conductor.

This application is a division of application Ser. No. 583,066, filed5/29/84, now abandoned, which in turn is a division of application Ser.No. 276,916, filed 6/24/81, now U.S. Pat. No. 4,454,278.

BACKGROUND OF THE INVENTION

It has been proposed to prepare polyesters from lower dialkyl esters ofterephthalic and isophthalic acid, ethylene glycol, and a higherpolyfunctional alcohol such as glycerine, for use as an electricalinsulating material (see U.S. Pat. No. 2,926,296 issued May 19, 1960).

It has also been proposed to prepare polyester-polyimides for use as awire enamel (U.S. Pat. No. 3,426,098, issued Feb. 4, 1969). According tothe latter patent the polyester/polyimide is prepared from (1)tris(2-hydroxy-ethyl)isocyanurate, (2) terephthalic or isophthalic acidor the lower alkyl esters thereof, (3) an aromatic diamine, e.g.,oxydianiline, or methylene dianiline, and (4) an aromatic carboxylicacid anhydride containing at least one additional carboxyl group, e.g.,trimellitic anhydride or pyromellitic anhydride. See also U.S. Pat. No.4,107,355.

While it is well known that polymers useful for wire enamels can be madeby reacting aliphatic diols and polyols with aromatic polycarboxylicacids or their alkyl esters, there has been lacking up to the presenttime, a practical synthesis for incorporating an aromatic nucleus as thebackbone of the polyol constituent. Attempts to substitute an aromaticpolyol, such as Bisphenol A, for the aliphatic diol in the synthesismentioned above have met with little or no success.

We have now discovered that the desirable properties possessed by anaromatic polyol, such as Bisphenol A, can be incorporated into a polymerbackbone, by reacting an aromatic ester of an aromatic dicarboxylic aciddirectly with the desired aromatic polyol, such as Bisphenol A. In suchreaction, the phenol forming the aromatic ester is smoothly eliminated,as a by-product and the desired reaction is carried out easily tocompletion.

SUMMARY OF THE INVENTION

Thus, according to the present invention there are provided polyesters,polyester/polyamides and polyester/polyamide/polyimide polymers whichfurnish wire enamel coatings of higher heat resistance and a smoothersurface which are superior to present enamel coatings.

According to one embodiment of the subject invention, aromatic ester ofa dicarboxylic acid such as diaryl terephthalate or diaryl isophthalateor mixtures thereof, for example, diphenyl terephthalate or diphenylisophthalate is reacted with an aromatic polyol, such as bisphenol A,bisphenol F, resorcinol, phloroglucinol, mesitol, and the like. Thearomatic polyol starting materials must have di-functionality, and, forcurability they can contain at least some tri or higher functionality.Suitable are phloroglucinol, pyrogallol, tri- ad tetra-hydroxy-biphenylor napthalene, and molecular-weight novolac resin.

By reacting the aromatic esters of the dicarboxylic acid with mixturesor combinations of aromatic polyols and amines there are obtainedpolyester/polyamide/polyimide polymers. Tri (or higher)-functionality atleast in part is also essential for curing here too.

If in place of the aromatic ester of dicarboxylic acids there issubstituted BPADA (the reaction product of bisphenol A and phthalicanhydride), polymers with an aromatic ether functionality are obtained.

DESCRIPTION OF THE INVENTION

To form the polymers of the subject invention, there is heated at anelevated temperature, (for example, at about 200° C. to about 270` C.for about 2 hours to about 7 hours, at a pressure of about oneatmosphere) (a) a diaryl terephthalate or diaryl isophthalate ormixtures thereof with (b) the aromatic polyol component, for example apolyhydric phenol and THEIC, or a mixture of (b) and (c) an aromaticdiamine, or with a mixture of (b) and (c) and (d) a triaryl mellitate,or a copolycarbonate of any of the foregoing including units derivedfrom (e) a diaryl carbonate.

When the reaction is carried with (b), polyesters are obtained. When thereaction is carried out with a mixture of (b) and (c) polyester/amideand polyester/amide/imide polymers are obtained. Of course, atrifunctional compound, like (d) a triaryl mellitate is needed for theimides.

The compositions employed in the present invention may be described interms of "equivalent percent." This term can be defined as follows:

The term "equivalent" as used in the present application refers to thenumber of moles of a substance multiplied by the number of functionalgroups present in the structure. Thus, the number of equivalents ofdiphenyl terephthalate in a quantity of diphenyl terephthalate is thenumber of moles of diphenyl terephthalate present times two. The numberof equivalents of bisphenol A present in a given quantity of bisphenol Ais the number of moles of bisphenol A present in the quantity multipliedby two. The number of equivalents of the aromatic diamine present in agiven quantity of the diamine is the number of moles of the aromaticdiamine present in the quantity multiplied by two. The term "equivalentpercent" as used in the present application refers to the number ofequivalents of a particular reactant divided by the total number ofequivalents of all reactants times one hundred.

As is conventional in the prior art, the equivalent ratio of hydroxylgroup to carboxyl groups in the starting products to produce the esterresins should amount to between 1.6 and 2.5. This equivalent ratiopreferably amounts to at least about 1.8. The upper limit is preferablyat 2.3.

The aryl esters of carboxy groups used for calculating the equivalentratio of hydroxyl group to carboxyl groups are only those (optionallyesterified, i.e., potential) carboxyl groups of the carboxylic acidswhich are still available for a transesterification reaction with thepolyol component for for an ester/amide interchange for the reactionwith the polyamines used for this purpose.

Conventional transesterification catalysts can be used, e.g., zincacetate, antimony trioxide, lithium hydroxide metal amine complexcatalysts and the like, at amounts of, for example 0.001 to 8% by weightbased on the weight of the composition.

The term "functional group" as used in the present application refers toa carboxyl group (--COOH), an ester group (--COOR) where R stands foraryl, a hydroxyl group (--OH), or an amino group (--NH₂).

As examples of diaryl terephthalates and isophthalates it is preferableto employ diphenyl terephthalate and diphenyl isophthalate.

As aromatic polyols it is preferable to employ for example, suchpolyhydric phenols as bisphenol A, bisphenol F, resorcinol,phloroglucinol, and tris- or higher poly-phenols such as novolac resins.

Examples of preferred aromatic diamines are methylene dianiline andoxydianiline. Other examples are 3,3' diaminodiphenyl,4,4'-diaminodiphenyl, diaminodiphenyl ketone and diaminodiphenylsulfone.

As a polyimide forming component it is preferable to employ a triarylmellitate, such as triphenyl mellitate.

As a polycarbonate forming component it is preferable to employ a diarylcarbonate, such as diphenyl carbonate.

The polyesters or polyester/polyamides comprising the subject inventionare used as a wire enamel. They are preferably employed in a solventsystem. Any suitable solvent can be employed, a preferred example beingcresylic acid or N-methylpyrrolidone. They are used to insulate anelectrical conductor, for example copper, silver, aluminum or stainlesssteel wire in conventional fashion. Thus wire speeds of 18 to 40feet/min. can be used with wire tower temperatures of 240° to 440° C.,usually with a final temperature of about 400° C. The build up of enamelon the wire can be 0.001 to 0.010 of an inch and in normal practiceabout 0.003 of an inch.

The subject invention is further described in examples which follow.These examples are given by way of illustration only and are not to beconstrued as limitations thereof. Many variations are possible withoutdeparting from its spirit and scope.

The results of actual wire coating tests using wire enamels of the typesset forth in the following examples are shown below.

The electrical conductor being coated is a copper magent wire 0.0403inch in diameter, the coating then being cured in a 15 foot tall gasfired tower having a bottom temperature of 245° C. and a top temperatureof 400° C. The wire after coating and curing is visually inspected forsmoothness and tested for burnout, which is an indication of theresistance to high temperature in the winding of a stalled motor. Suchtests are well known to those skilled in the art and are described, forexample, in U.S. Pat. Nos. 2,936,296; 3,297,785; and 3,555,113, andelsewhere. The dissipation factor (D.F.) is carried out by immersing abent section of coated wire in a molten metal bath and measuring to 60to 1,000 hertz by means of a General Radio Bridge, or its equivalent,connected to the specimen and the bath. The values are expressed in unitof % at the specified temperature in degrees Centigrade (ReferenceNational Electrical Manufacturers Association Publ. No. MW 1000 Part 3,paragraph 9.1.1). Cut through temperature is carried out by positioningtwo lengths of wire at right angles, loading one with a weight andraising the temperature until thermoplastic flow causes an electricshort and the values are expressed in units comprising degreesCentigrade at 2,000 g. (References NEMA method 50.1.1). Dielectricstrength is determined on twisted specimens to which are applied 60hertz voltage until breakdown occurs. The breakdown voltage is measuredwith a meter calibrated in root-mean-square volts. The values areexpressed in units comprising kilovolts (kv) (Reference NEMA Method7.1.1).

EXAMPLE 1

The following mixture is introduced in a reaction vessel to prepare apolyester resin:

0.4403 moles (140 grams) of diphenyl terephthalate;

0.1887 moles (60 grams) of diphenyl isophthalate;

0.0699 moles (30.6 grams) of triphenyl trimellitate;

0.0143 moles (3.05 grams) of diphenyl carbonate; and

0.6860 moles (156.4 grams) of bisphenol A

The mixture is slowly heated at a temperature ranging from about 120° C.to about 180° C. until the reactants are melted. At this point 34.3 μLof a 0.1M solution of lithium hydroxide is added as a catalyst and themixture heated at a temperature of from about 200° C. to about 230° C.under variable pressure for about 4 to about 7 hours. The resultingresin is then isolated and cooled.

In preparing a preferred wire enamel composition in accordance with thepresent invention, the polyester resin is dissolved in cresylic acid inthe proportion of about 35% of resin to about 65% of cresylic acid at atemperature of from about 140° C. to about 150° C.

After the resin is completely dissolved the resulting solution is cooledto about 90° C. and 7.5 grams of a blocked polyisocyanate (Mondur SH) isadded. This solution is then further cooled to about 50° C. at whichpoint 3.75 grams of tetra isopropyl titanate dissolved in 10 grams ofcresylic acid is added.

The resulting enamel is then coated on wire, for example, by the dieapplication procedure using No. 18 AWG copper wire and passing thecoated wire 7 times through a 15 foot vertical wire tower, to prepare asample suitable for testing. The test results are as follows:

                  TABLE 1                                                         ______________________________________                                        Polyester Wire Properties of Enamel                                           Comprising Diphenyl Terephthalate, Diphenyl Isophthalate,                     Bisphenol-A, Triphenyl Trimellitate and Diphenyl                              Carbonate.                                                                    ______________________________________                                        Speed (ft/min.)    40                                                         Dissipation factor                                                            170° C.     1.4                                                        220° C.     4.1                                                        Cut Thru °C., 2000 g                                                                      331                                                        Burnout OFM        7.12                                                       Dielectric Strength, KV                                                                          2.4                                                        ______________________________________                                    

The wire was exceptional in its cut through and burnout resistance.

EXAMPLE 2

The following mixture is introduced in a reaction vessel to prepare apolyester amide/imide resin:

0.629 moles (200 grams) of diphenyl terephthalate;

0.343 moles (150.3 grams) of triphenyl trimellitate;

0.265 moles (52.5 grams) of methylene dianiline;

0.0223 moles (4.9 grams) of diphenyl carbonate; and

0.8163 moles (186.1 grams) of bisphenol A

The procedure is the same as in Example 1, except 41 ∥L of a 0.1Msolution of lithium hydroxide is added as a catalyst.

In preparing a wire enamel composition in accordance with the presentinvention, the polyester amide/imide resin is dissolved inN-methylpyrrolidone (NMP) in the proportion of about 29% resin to about71% of NMP at a temperature of from about 140° C. to about 150° C.

After the resin is completely dissolved the resulting solution is cooledto about 90° C. and 8.6 grams of blocked polyisocyanate (Mondur SH) isadded. This solution is then further cooled to about 50° C. at whichpoint 4.3 grams of tetra isopropyl titanate dissolved in 10 grams of NMPis added.

The resulting polymer is then applied as an enamel on a wire asdescribed in Example 1. The test results are as follows:

                  TABLE 2                                                         ______________________________________                                        Polyester Amide/Imide Wire                                                    Properties of Enamel Comprising Diphenyl Terephthalate,                       Triphenyl Trimellitate, Methylene Dianiline,                                  Bisphenol-A, and Diphenyl Carbonate.                                          ______________________________________                                        Speed (ft/min.)     40                                                        Dissipation Factor 220° C.                                                                 4.6                                                       Cut Thru °C., 2000 g                                                                       372                                                       Burnout OFM         8.90                                                      Dielectric Strength, KV                                                                           6.5                                                       ______________________________________                                    

The coated wire exhibited good cut through and burnout.

The patents mentioned above are incorporated herein by reference. Theforegoing detailed description will support many variations to thoseskilled in this art. All such variations are within the full scope ofthe appended claims.

We claim:
 1. A polyester resin comprising the reaction product of:(a) anaromatic ester of a dicarboxylic acid; (b) polyol consisting essentiallyof aromatic polyol; (c) tri or higher functionality material whereinsaid functionality is independently selected from the group consistingof --COOH; --NH₂ ; --COOR where R is aryl; and --OH; and (d) a blockedpolyisocyanate.
 2. The polyester resin of claim 1 wherein said tri orhigher functinality material is selected from the group consisting oftriaryl mellitate, novolac resins, andtris(2-hydroxy-ethyl)isocyanurate.
 3. The polyester of claim 1 which isdissolved in a solvent.
 4. The polyester of claim 1 which is cured on aconductor.
 5. A polyester resin consisting essentially of the reactionproduct of:(a) an aromatic ester of a dicarboxylic acid; (b) polyolconsisting essentially of aromatic polyol; (c) tri or higherfunctionality material wherein said functionality is independentlyselected from the group consisting of --COOH; --NH₂ ; --COOR where R isaryl; and --OH; and (d) a blocked polyisocyanate.